Latent Fingerprint Chemical Imaging by Mass Spectrometry

摘要

Latent fingerprints (LFPs) are distributions of exogenous and endogenous chemicals in a particular pattern. They potentially contain more forensic information than the simple identification of the subject; they may contain evidence of contact with explosives or substances of abuse. Chemically specific surface analysis methods are required to reveal the full information contained in LFPs. Such techniques often require de-rivatization (1) or addition of fluorescent or other tags (2). Mass spectrometry (MS) imaging (3) provides spatially specific chemical composition information on surfaces. Unlike other MS imaging methods, desorption electro-spray ionization (DESI) MS (4) offers chemical imaging capabilities through mass spectra recorded without sample preparation from ordinary samples in their native environment In DESI, a solvent is electrosprayed onto the surface. Secondary scattered droplets are generated and evaporated, and their constituents mass analyzed. A mass spectrum is recorded in turn at each point on the surface by rastering the stream of charged droplets across the surface (5). This method has a spatial resolution of 150 urn. Spectroscopic techniques such as Fourier transform infrared (FTIR) and Raman also provide ambient imaging analysis and have better spatial resolution but poorer chemical specificity than MS techniques (6). However, the use of these methods to reconstruct fingerprint images from ordinary surfaces based on exogenous compounds has not been demonstrated (6).